1. Field of the Invention
This invention relates to electric lamps and, more particularly, to electric lamps with threaded bases.
2. Description of the Prior Art
Tungsten halogen lamps are known in the art and have an inner capsule which contains the tungsten halogen apparatus, and an outer envelope which guards against possible non-passive fracture of the inner capsule, and shields the user from the high surface temperature of the inner capsule. The inner capsule is mounted on a frame inside the outer envelope, with the frame acting as an electrical connection for the inner capsule. Tungsten halogen lamps can produce a higher quality light, be more efficient, and have a longer life than ordinary filamented lamps.
During assembly, the frame and inner capsule are inserted in the outer envelope, and a threaded base is screwed onto the outer envelope. The threaded base pinches exterior arms of the frame against an envelope neck to make electrical contact and hold the frame in place. To make good electrical contact, and to ensure the base is not subsequently unthreaded, the frame-to-base contact has been made by a sharp point, directed in the threading direction. As the base threads over the frame, the frame points dig progressively deeper into the base. In final position, the frame points are well embedded in the base, ensuring electrical contact, and are pointed against the unthreading of the base to prevent removal of the base. Because of variations in the pointed ends, the lengths of the frame components, molded glass dimensions and similar causes, the frame ends do not always contact the base equally. The frame can then be twisted in the outer envelope, leaving the inner capsule misaligned and presenting both a cosmetic problem and a mechanical problem. The misaligned inner capsule can knock against the outer envelope during shipment and break. The life of the inner capsule may also be affected by the irregular heat flow around the adjacent outer envelope. There is thus a need for a support frame that consistently centers the inner capsule in the outer envelope.
Double envelope, tungsten halogen lamps are, in manufacture, assembled by hand threading the base to the lamp neck. The torque characteristic of lamps with pointed frame ends is not a linear force, but is an increasing, and perhaps, even an accelerating force. The high torque needed to thread the base to its final position may lead to injuries from repeated high stress of the assemblers' fingers, hands, or wrists. By reducing the diameter of the support frame wire, the support frame may be made more flexible, but a more flexible support frame allows greater sway in the assembled lamp. Greater flexibility in the support frame is also likely to result in a bent, or distorted support frame. There is then a need for a double envelope electric lamp with a low assembly torque support frame for the internal capsule that is unlikely to sway or be distorted.
Standard lamps have frequently been sealed by cementing or epoxying the threaded metal base to the outer glass envelope. Fluid or paste glues and cements are not easy to work with in an assembly line operation. Inadequate gluing may occur, allowing the base to open, while excessive gluing may leave the lamps cosmetically unacceptable. Glues and cements are also usually relatively expensive materials. There is thus a need for a capsule lamp having the metal base fixed to the outer envelope without glue or cement.
Small portions of the threaded base have also been peened into slots formed in the lamp envelope. Peening requires that the lamp be properly oriented, so the peenings properly complement the preformed envelope slots. Alignment of peening apparatus and envelope slots consumes time, and machinery is required to properly execute such alignment. Peening regularly results in broken product, where the peening strike is excessive. Alternatively, less peening force can yield lamps with bases that loosen. There is thus a need for a lamp with a mechanically sealed envelope and base connection that does not require alignment of peening apparatus and envelope slots.
Hand assembly of lamps does not usually lead to strong mechanical couplings between bases and envelopes. On the other hand, a lamp envelope, being made of glass, necessarily is fragile, and a mechanical coupling made by a machine often leads to fracture of the lamp envelope, and wasted product. There is then a need for a machine-made mechanical coupling between the outer envelope of a capsule lamp and a threaded metal base, which coupling reduces or eliminates waste through fracturing of envelopes.
Examples of the prior art are shown by the following U.S. patents:
U.S. Pat. No. 3,194,625 issued to G. K. Danko on Jul. 13, 1965, for an Electric Lamp with Unitary Inner Envelope and Stem Assembly and Manufacturing Thereof, shows a threaded base lamp with an internal capsule integral with an outer envelope. The threaded base is cemented to the outer envelope.
U.S. Pat. No. 3,243,634 issued to F. A. Mosby on Mar. 29, 1966, for an Electric Lamp and Support Web, shows a threaded base lamp with an internal capsule supported from the threaded base. The threaded base is cemented to the outer envelope with an epoxy.
U.S. Pat. No. 4,657,809 issued to R. G. Blaisdell et al. on Mar. 3, 1987, for Electric Lamp with Self-Mounting Frame-Assembly and Method of Constructing Same, shows a threaded base lamp with an internal capsule. The internal capsule is supported on a wire frame that has spiked ends bent around the opening of the outer envelope. The threaded base is threaded to the outer envelope, causing the spiked ends to be compressed and pointed into the base. The spikes resist unthreading of the base from the outer envelope.
U.S. Pat. No. 4,959,583 issued to Vito J. Arsens et al., on Sep. 25, 1990, for Reflective Lamps Having An Improved Light Source Mounting Arrangement, shows a threaded base lamp with an internal capsule. The threaded base is coupled to the outer envelope by a high temperature resistive adhesive.